(Android does this).  Fix logging for executable mappings that have no
file associated.  Be more consistent with use of uintptr_t.
Review URL: http://codereview.chromium.org/125183

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2187 ce2b1a6d-e550-0410-aec6-3dcde31c8c00